The independent lawyer who is leading the review of the state drug lab scandal said Friday that he has identified nearly 500 additional defendants who are in jail awaiting trial or on parole based on questionable evidence.

The new assessment raises the stakes as law enforcement and court officials scramble to resolve what has grown into a nightmare for the criminal justice system.

And amid the growing concerns over the lab, a Roxbury Municipal Court judge dismissed drug charges Friday against a Boston man following a trial that centered in large part on evidence that may have been tainted by the scandal.

David Meier, the lawyer ­appointed by Governor Deval Patrick to comb through the 34,000-plus cases that could be at issue, said at an afternoon press conference at the State House that 335 people are ­being held on bail awaiting ­trial, and that another 144 are on parole based on evidence handled by a disgraced state chemist.

In addition, 319 juveniles were committed to a detention center at one point based on ­evidence handled by the chemist, Annie Dookhan.

The announcement was made just over two weeks after Meier identified 1,141 people who are serving sentences in state prison or county jails based on evidence that Dookhan handled.

Meier prioritized review of those cases to ensure that no one was being jailed on false ­evidence, and identification of the ­additional cases has added to the urgency and workload, he said. “We’re working to identify ­every individual . . . whose liberty might be restricted in some way because they’re on parole, they’re on probation, as a result of a drug case that this chemist may have worked on.”

Jonathan Wiggs/Globe Staff

Della Saunders, who worked with disgraced state chemist Annie Dookhan, testified at Drumgold’s trial.

Meier said officials have made no determination on the integrity of the evidence in the cases, saying that finding should go before the courts. But he said defense lawyers, prosecutors, and his staff have been working in a “boiler room” setting to quickly identify cases that could be at issue and to ­notify defendants, in an effort to maintain the integrity of the criminal justice system. Officials are reviewing defendants who are on probation based on cases in which Dookhan was ­involved, he said. “We’d rather be overly inclusive than not ­include one person, that’s how important it is,” he said.

Meier said that the bulk of the 34,000 cases will involve people who have served their prison sentences, completed probation, or had their cases continued without a finding in district court.

He also said Friday that special court sessions designed to consolidate challenges of drug convictions based on Dookhan’s involvement, expected to ultimately be in the thousands, will begin with hearings Monday in Suffolk Superior Court. Superior courts in other counties will also hold hearings.

Defendants have already challenged their sentences in Boston Municipal Court. On Friday, four defendants saw their sentences stayed and were given strict curfews while their cases are being reviewed.

Suffolk District Attorney Daniel F. Conley said he has ­appointed three veteran prosecutors to handle cases affected by the scandal, and they will ­review postconviction motions to determine whether defendants should be released, have their convictions reversed, or remain behind bars.

The drug lab scandal has had one of the worst effects on the criminal justice system in recent time. Dookhan, 34, of Franklin, was a chemist at the Department of Public Health-run laboratory in Jamaica Plain from 2003 to June 2011, when her handling of evidence was first questioned. She left the laboratory in March. This past summer, State Police who took over the laboratory found that Dookhan’s wrongdoing was far more widespread than initially believed, putting into question the more than 60,000 samples, involved in more than 34,000 cases, that she had handled.

Federal officials also disclosed this week that at least 100 federal cases and possibly as many as 200 could be in jeopardy based on Dookhan’s involvement.

As a chemist, Dookhan was responsible for testing drugs, determining their weight, and confirming tests done by other chemists. An inves­tigation found that in some instances she allegedly said a substance was cocaine when other tests showed it was not. On several occasions, she allegedly sprinkled cocaine on a substance that did not test positive.

She has been charged in criminal court for two such ­occasions of falsifying evidence. She was also charged with falsely claiming to law enforcement officials that she has a master’s degree in chemistry. She has pleaded not guilty and been ­released on $10,000 cash bail.

Defense lawyers have ­argued that Dookhan’s work has jeopardized the integrity of all cases handled at the laboratory during her years there. Dozens of defendants have been released on reduced bail or had their prison sentences suspended while their cases are being reviewed, and lawyers have been petitioning the courts for their clients’ release on a daily basis.

On Friday, a Boston man had his drug charges dismissed in a case in which his lawyer challenged the quality of drug evidence based on Dookhan’s involvement.

Shawn Drumgold, who in 2009 won a multimillion-dollar wrongful conviction lawsuit against Boston after serving 15 years in prison for a murder he says he did not commit, was ­accused of drug possession following a raid on a Roxbury home in 2011. Judge David ­Weingarten did not mention Dookhan in deciding to dismiss the drug case, ruling instead that prosecutors failed to link Drumgold to the crack cocaine and heroin found in the home.

But the trial provided for the first time a detailed look at the kind of work Dookhan did. Several of her former colleagues were called to testify on how they and she handled evidence. Dookhan was summoned to testify, but invoked her Fifth Amendment right against self-incrimination.